1. Field of the Invention
This invention relates to a dewaxing method of a metal or ceramic molded body formed through a plastic molding.
2. Description of the Prior Art
There is a method of manufacturing a molded body which comprises kneading a metal or ceramic powder with a dispersion medium such as plastic resin or wax under heating to obtain a compound having plasticity, and molding the compound by extrusion molding, injection molding, press molding or the like. The molded body is heated up to 400.degree. to 600.degree. C. to remove the dispersion medium by converting it into gases through thermal decomposition. Thereafter, the molded body is heated in vacuo or in an atmosphere of hydrogen gas, nitrogen gas, argon gas or the like to progress densification, and a sintered body is obtained.
In the above conventional dewaxing method of removing the dispersion medium, a great quantity of gas is generated by the thermal decomposition of the dispersion medium, and the gases are necessary to be removed from the inside of the molded body. Therefore, the temperature must be elevated slowly, and it requires about 150 hours. When the rate of temperature rise is erroneously set, defects such as cracking and expansion are generated in the molded body.